1. Field of the invention
The invention relates to the field of power electronics. It is based on a filter arrangement which is connected to the load side of a converter circuit arrangement, in which case the converter circuit arrangement has n phases and comprises n load connections to which the filter arrangement is connected, which filter arrangement comprises at least one series inductance per load connection. A filter arrangement of this generic type has already been described in European Patent Applications EP 0 682 401 A1 and EP 0 682 402 A2.
2. Discussion of Background
In the documents mentioned above, an LC low-pass filter which is possibly lossy due to resistances is inserted between the load connections and a load. The connections of the capacitors can either be joined together to form a star point, or can be connected to the positive and negative connections of the intermediate circuit. The circuit arrangement described in these documents are preferably used for low-voltage applications. EP 0 318 790 also discloses a high-pass filter for a filter arrangement for a cable which is connected to converters.
The aim of a load-side filter is to achieve an output voltage which is as sinusoidal as possible. One ay would be to design the filter to be as large as possible. However, this would have a number of important disadvantages. If the filter capacitor were short-circuited, the relevant capacitor, and all the others connected in parallel, would be discharged through the short-circuit. Furthermore, the short-circuit can result in large sudden torque changes on the connected motor, and high overvoltages on the motor windings and filter capacitors. As consequential faults, other short circuits can occur, so that a large amount of energy is suddenly released, which can result in destruction. The greater the filter capacitance is chosen to be, the greater is the amount of energy which must be destroyed in a deflective filter can. In consequence, the filter can can burst, and isolation oil can escape and contaminate the environment.